(i) Field of the Invention
The present invention relates to a sheet feeding apparatus in which sheets for printing stored in a sheet storage unit is taken out and fed out sheet by sheet by a sheet feed roller rotated by a motor.
(ii) Description of the Related Art
For example, as a sheet feeding apparatus mounted on an ink jet printer, a constitution has heretofore been known in which a sheet feed roller is brought in contact with a surface of a plurality of laminated printing sheets and rotated by a motor to feed out the printing sheet in a predetermined direction.
In this type of sheet feeding apparatus, it is conventional to use a stepping motor as the motor for rotating the sheet feed roller. Moreover, for example, when there is a sheet feed request by an input of printing job data from the outside, the motor is driven to rotate the sheet feed roller, and one of the plurality of printing sheets stored (laminated) in a predetermined storage position is taken out. This taken printing sheet is successively fed out to a registration position where sheet transfer at a printing operation is started by the sheet feed roller.
In this registration position, a transfer roller is disposed to transfer the sheet at the printing operation. After the tip ends of the printing sheets fed out by the sheet feed roller are aligned in this registration position, the printing sheets start to be transferred by the transfer roller. Moreover, while the printing sheet is transferred by the transfer roller, a desired image (printing job data) is printed on the printing sheet.
It is to be noted that a registration sensor for detecting the tip-end position of the sheet being fed is disposed in a predetermined position on a sheet feed path extending to the registration position from the storage position from which the sheet is taken out.
Therefore, after the printing sheet is removed from the storage position, the stepping motor is driven until the tip-end position of the sheet is detected. In this case, a feed amount sufficiently longer than the length of the sheet feed path extending between the storage position and registration sensor is set to a target value. Subsequently, after the detection by the registration sensor, the target feed amount is successively set in accordance with a distance, known beforehand, between the detected position and registration position, and the stepping motor is accordingly driven. As a result, when the tip end of the sheet reaches the registration position, the driving of the stepping motor stops to stop the rotation of the sheet feed roller, and thereby the sheet feed operation of the printing sheet is completed.
In recent years, there has been an increasing demand for the speeding-up of the sheet feed operation in the sheet feeding apparatus or noise reduction at a sheet feed operation. However, in the sheet feeding apparatus in which the stepping motor is used as a driving source as described above, it is very difficult to achieve both the speeding-up and noise reduction.
That is, as well known, the stepping motor rotates by each predetermined step angle in response to a pulse signal. Therefore, the rotation speed has its upper limit. When a pulse rate is increased so as to be not less than a predetermined value, the motor steps out. There is a possibility that rotation control itself becomes impossible.
Additionally, in operation principle in which the motor rotates little by little in response to the pulse signal, there is a tendency that the accelerated rotation speed results in much noise.